Energy storage and catalytic behaviour of cmWave assisted BZT and flexible electrospun BZT fibers for energy harvesting applications

High-performance lead-free Barium Zirconium Titanate (BZT) based ceramics have emerged as a potential candidate for applications in energy storage, catalysis for electro chemical energy conversion and energy harvesting devices as presented in this work. In the present study hybrid microwave sintered BZT are studied for dielectric, ferroelectric and phase transition properties. BZT ceramic exhibits tetragonal structure as confirmed by the Retvield refinement studies. XPS studies confirms the elemental composition of BZT and presence of Zr. Polarization versus electric field hysteresis loops confirms the ferroelectric behaviour of BZT ceramic. Encouragingly, the BZT showed a moderate energy storage efficiency of 30.7 % and relatively good electro chemical energy conversion (HER). Excellent catalytic activity observed for BZT electrode in acid medium with low Tafel slope 77 mV dec-1. Furthermore, electrospun nanofibers made of PVDF-HFP and BZT are used to make flexible piezoelectric nano generators (PENGs). FTIR studies show that the 16 wt% BZT composite ink exhibits a higher electroactive beta phase. The optimized open-circuit voltage and short circuit current of the flexible PENG exhibits 7Vpp and 750 nA under an applied force of 3N. Thus, flexible and self-powered BZT PENGs are alternative source of energy due to its reliability, affordability and environmental-friendly nature.


Energy storage and catalytic behaviour of cmWave assisted BZT and flexible electrospun BZT fibers for energy harvesting applications
High-performance lead-free Barium Zirconium Titanate (BZT) based ceramics have emerged as a potential candidate for applications in energy storage, catalysis for electro chemical energy conversion and energy harvesting devices as presented in this work.In the present study hybrid microwave sintered BZT are studied for dielectric, ferroelectric and phase transition properties.BZT ceramic exhibits tetragonal structure as confirmed by the Retvield refinement studies.XPS studies confirms the elemental composition of BZT and presence of Zr.Polarization versus electric field hysteresis loops confirms the ferroelectric behaviour of BZT ceramic.Encouragingly, the BZT showed a moderate energy storage efficiency of 30.7 % and relatively good electro chemical energy conversion (HER).Excellent catalytic activity observed for BZT electrode in acid medium with low Tafel slope 77 mV dec-1.Furthermore, electrospun nanofibers made of PVDF-HFP and BZT are used to make flexible piezoelectric nano generators (PENGs).FTIR studies show that the 16 wt% BZT composite ink exhibits a higher electroactive beta phase.The optimized open-circuit voltage and short circuit current of the flexible PENG exhibits 7Vpp and 750 nA under an applied force of 3N.Thus, flexible and self-powered BZT PENGs are alternative source of energy due to its reliability, affordability and environmentalfriendly nature.
Many researchers focus on sustainable green energy conversion and storage systems to reduce energy crises and global air pollution.Due to increasing energy demand and higher energy prices the world's only concern is energy.In the next two decades, the global energy demand is anticipated to double.Because of this, it became necessary to develop numerous methods for the generation of energy and its storage.Piezoelectric materials are potential candidates for energy harvesting and storage applications 1 .Though Lead zirconium titanate (PZT) and other lead based piezoelectrics are commertially accepted, EU and other Western nations have baned the usage of lead in many commodities due to its toxicity.due to this resolution, biocompatible and ecologically friendly lead-free piezoelectric material are in demand due to lead toxicity.Lead free materials with low density can also have advantages in several electronic device applications such as transducers, sensors, energy conversion and storage etc. Various materials are currently under reconsideration as potential substitutes for PZT, which may be effective in specific situations 2 .So, the present research is focused on lead free materials and finding other sources of energy that are cleaner and last longer, like solar, wind, hydel, mechanical movements, magnetic fields and electrochemical etc.So, the present research is focused on finding other sources of energy that are cleaner and last longer, like solar, wind, hydel, mechanical movements, magnetic fields and electrochemical etc 3 .Therefore, renewable energy contributes to the evolution of various energy storage devices.This includes all energy storage devices like batteries, dielectric and electrochemical capacitors and electrolyzers 4 .The energy storage mechanism and flow of charges influence the power density, energy storage density and charge-discharge time of the devices.Batteries possess a high energy density but low power density 5 .The reason for this is the slow 4.0239 Å, c = 4.0110 Å respectively.The unit cell volume of BT and BZT are 64.6695 and 64.94 Å 3 respectively.The goodness of fit ( χ 2 ) value is 2.48 indicating a best fitting refinement of BZT.The average crystallite size of the BT and BZT are estimated by Scherrer formula given by the following equation 29 .
It is noticed that the estimated D value and unit cell volume of BZT is higher compare to BT.It may be due to addition of Zr to the BT and high sintering temperature of BZT compare to BT.The average crystallite size of the BT and BZT are 60, 91 nm respectively.The above values suggests diffusion of Zr ion in the unit cell.However, the above findings are further verified by XPS studies.

XPS
To get a better understanding of the binding energies associated with the various chemical states of the material and presence of Zr in parent BT ( BaTiO 3 ), X-ray photoelectron spectroscopy (XPS) is recorded.Fig. S2a,b (sup- plementary information) shows the survey spectrum of BT-1250 and BZT-1300 ceramics.The binding energies of BZT-1300 are tabulated in Table 1. Figure 1b-e depicts high-resolution spectra of BZT-1300 individual elements (Ba, Zr, Ti, O).The doublet spectra of Ba in BZT are Ba3d 3/2 , and Ba3d 5/2 are fitted at higher energy 793.82 eV and lower energy 778.53 eV, respectively as shown in Fig. 1b.Similar binding energy peaks have been reported by Fahad et al. 30 for the Ba3d 5/2 and Ba3d 3/2 , where the former occurring at a lower energy of 778.34 eV and the latter occurring at a higher energy of 793.71 eV.This pattern of peaks is characteristic of the 2 + oxidation state  www.nature.com/scientificreports/ of barium ions.Fig. 1c depicts high-resolution spectra of Ti.Due to the spin-orbit coupling, the high-resolution doublet spectra of Ti2p split into two peaks at 457.87 eV and 463.85 eV, corresponding to Ti2p 3/2 and Ti2p 1/2 , respectively.The difference in binding energy between the major peaks of Ti2p in BZT is 5.98 eV, which is greater than the major binding energy peaks difference of Ti2p peaks of BT.The binding energy changes in Ti2p spectra in BZT ceramic is an evidence of Zr substitution at the Ti-site.The Zr substitution in the Ti site cannot create the reduction of Ti 4+ to Ti 3+31 .Fig. 1d depicts high-resolution spectra of Zr.The high-resolution spectra of Zr3d 5/2 and Zr3d 3/2 are fitted at 180.94 eV and 183.34 eV, respectively.The difference in binding energy between the major peaks of Zr3d in BZT is 2.4 eV which is due to spin-orbit coupling the Zr ion substitution in the Ti site 30 .Fig. 1e depicts high-resolution spectra of O1s exhibit two overlapping peaks at 529.27 eV and 530.61 eV.Similar type of results were presented earlier by Chakrabarti et al. 32 .

Dielectric studies
The temperature-dependent dielectric constant and loss behaviour of microwave-sintered BZT-1250, BZT-1275, BZT-1300 are investigated systematically in the range of temperature (30 to 120 • C), and frequency range of 1000 Hz to 1 MHz it is shown in Fig. S3a-d (supplementary information) and Fig. 2a,b.The relative permittivity and loss of BZT depends on several factors like purity, microstructure, chemical composition and sintering temperature etc 33,34 .It is noticed that the sintering temperature is directly proportional to dielectric constant and inversely proportional to T c and Tan d.The reason may be the impure phase ( ZrO 2 ) is presented at BZT-1250, BZT-1275.The dielectric results are well agree with structural studies.The dielectric constant and Tan d values are tabulated in Table 2. Figure 2a (BZT-1300) shows that up to 90 • C, the dielectric constant is almost the same at all frequencies.This is due to the weak and constant charge carrier feedback at these temperature ranges ( 30 to 90 • C) 35     Ferroelectric properties and energy storage properties of ferroelectric capacitors are determined by P-E hysteresis loops.The circum triangle formed by P s , P r and the first quadrant curve represents the energy storage density (W rec ).The first quadrant area under the curve represents the material energy loss density (W loss ).From the P-E hysteresis loops the energy-loss density (W loss ), recoverable energy-storage density (W rec ), and the efficiency of the bulk ceramic capacitor are estimated from the following equations 9,36 .
where E is the applied electric field, P max is the maximum polarization, P r is the remnant polarization.The energy density values of the microwave-sintered BZT ceramics are found to be moderate energy storage.The energy storage efficiency of the BZT electro ceramic depends on loss and recoverable energy.The Polarization (P max ), coercive field (E c ) and remanent polarization (P r ) values of perovskite BZT is directly proportional to the applied electric field.But the storage efficiency of the BZT is inversely proportional to the applied electric field.At low-applied electric fields, the storage efficiency ( η ) is high compared to higher fields.The recoverable energy and loss energy with the variation of the electric field of BZT is shown in the Fig. 2d-g.Despite high dielectric constant the observed low energy storage values are attributed to low squreness factor of the PE loops.The P r , P max , E c , W loss , W rec and efficiency values of BZT with the variation of electric field are tabulated in Table S1.Table 3 shows the comparison of energy storage efficiency with literature.
(2) R sq = P r P s

FTIR analysis
Figure 3a depicts the FTIR spectra of the BZT/PVDF-HFP composites.Bands at 763 cm −1 , 795 cm −1 , and 976 cm −1 are characteristic of the non-polar α phase of the TGTG.The TTTT confirmation of the polar electroactive β phase is responsible for the characteristic peaks at 841 cm −1 , 1276 cm −1 , and 1431 cm −1 .In the meantime, the band that can be found at 840 cm −1 is related to both the β and γ phases 28,43 .The non-polar α phase do not appear at all in the spectra of electro spun samples.In spite of this, the 840, 1276, and 1431 cm −1 bands, which correspond to the polar electro-active β phase, are present in the spectra of all electro spun samples.The polar electro active phase ( β phase) relative fraction of electrospinning fibers are calculated by the following Eq. ( 6).
In this scenario, it is assumed that the Lambert-Beer law governs the infrared transmittance.
where A β and A α are the absorbances at 841 and 763 cm −1 , and K β and K α are the absorption coefficients at those wavenumbers (6.1*104 and 7.7*104 cm 2 mol −1 , respectively). Figure 3a depicts the beta phase variation of composite fibers and pure polymer.The percentage of β phase F(β ) estimated from Eq. ( 6), of BZT/PVDF-HFP composite film increases with BZT ceramic load compared to the pure polymer film.The polar phase value reaches up to 83% when the content of BZT ceramic is 16 wt% , which is higher than the value for pure PVDF and other BZT ceramic loadings.Further addition (24 wt%) of BZT ceramic reduces the F(β ) value of the BZT/PVDF-HFP composite film due to segregation, it can be shown in morphology of composite fibres (SEM high load BZT image).The beta phase percentage of the composites are tabulated in Table S2 (supplementary information).Figure 3b depicts a mechanism of interaction between polymer and ceramic that could account for the observed increase in the relative content of the polar β phase.Also, zeta potential analysis resulted in a -Ve charge on the surface of BZT-1300 ceramic.The results are presented in Fig. 4a.Ceramic fillers with negative surface charges seems to increase the polar β phase of polymers, a phenomenon attributed to the interaction between the negatively charged particles and the PVDF -CH 2 groups.Thus, the electrostatic attraction/repulsion between -CH 2 /-and BZT (-Ve charge particles) and the CF 2 dipoles of polymer helps the PVDF-HFP chains to easily align in TTTT formation.Moreover, the attraction and repulsion forces play a significant role during the electrospinning process, which can enhance the polar β phase.In the present work BZT plays the significant role forming β phase.

SEM analysis
The dense and tightly packed grains are formed in BZT sintered at 1300 • C (see Fig. 4b.The average grain size of the BZT is 2.7 µ m as studied by the histogram images of ImageJ software.The water wave patterns noticed on the surface of the grains are suspected to be a ferroelectric domain layers.A deeper probing of the grain could confirm further details.Similar morphology was earlier reported by Fahad et al. 30 .The morphology of electro spun composites exhibited a high-quality smooth nanofiber without ceramic or polymer bead formation (Fig. 4c and Fig. S5a-c (supplementary information) except for 24 wt% ceramic loading.It is clearly seen that with an increase in BZT concentration, fibres showed a tendency to shrink in diameter.It may be due to change in viscosity of the solution and agglomeration of ceramic in the polymer matrix 44 .Similar types of results are published earlier by Athira et al. 28,45 .The distinct elemental mapping confirms all elements are uniformly distributed.It can be seen in Fig. 4d-i.

Device results
The focus of the work is to study the real time applications of the piezoelectric nano composites.To fabricate planner device, BZT composites are electro spun in to flexible fibers.The device is fabricated according to the schematic shown in Fig. 7.For mechanical strength, flexibility and to avoid interaction with the ambient atmosphere, the device is encapsulated with polyethylene terephthalate (PET).Further the encapsulation prevents slipping of the layers and ensures electrodes are intact during measurement.To characterise the device, the piezoelectric nanogenerator is placed on a vibration-free table to eliminate the possibility of a spurious voltage build up.The device was wrapped in aluminium tapes and grounded outside so electromagnetic waves wouldn't mess with the data, and works as a Faraday cage 46,47 .The output performance of the flexible piezoelectric nanogenerator is investigated systematically under the constant cyclic force of 3 N at 3 Hz frequency using a linear ( 6) mortar.When the BZT ceramic and PVDF-copolymer interact, charge density is created over the ceramic polymer (BZT-PVDF-HFP) composite, which causes surface charges to induce electrostatic interactions.The local stress results in spontaneous polarization of the piezo-electrically active beta-phase (Fig. 3b) 45,48 .The main causes of the polymer ceramic composite's transition from the nonpolar phase to the electroactive beta-phase are the (-CH 2 /-CF 2 ) bond stretching vibrations, the interaction of BZT ceramic dipoles with the polymer PVDF-HFP dipoles, and stress-induced polarization 49 .In this particular instance, the BZT ceramic plays the role of a nucleating agent for the formation of the polar crystalline phase within the PVDF-HFP/BZT ceramic composite 49 .Figure 5a depicts the schematic representation of the PVDF-HFP/BZT composite's working mechanism.If there is no mechanical impact from the outside, all dipoles in the composite (PENG) are randomly oriented, so there is no net dipole moment, as shown in Fig. 5(i).The crystal structure of the flexible piezoelectric nanogenerator PENG is deformed under stress, changes the dipolar distribution and results in potential across.A piezoelectric potential is created by the difference in potential between the two electrodes, which propels the flow of electrons through an external circuit from one electrode to another electrode.It leads to the + ve voltage.It is shown in Fig. 5(ii).The piezoelectric potential vanishes in a rapid way when the strain is released, and to make up for this, the electrons that have accumulated close to the electrode travel through the external circuit and back to the other electrode, which results in an electric signal travelling in the opposite direction leading to -ve potential (shown in Fig. 5(iii)).As a result, an alternating voltage is generated by the persistent vertical compression and release.The optimized output voltage of piezoelectric nanogenerators made from BZT (0, 8, 16, 24 wt%) under constant cyclic force of 3 N at 3 Hz frequency are presented in Fig. 5b.The output voltage is found to systematically increases with BZT load wt% of up to 16 wt%.Beyond which a declain in the output voltage is noticed which is as expected from the FTIR results.Fig. 5c depicts the output current of 16 wt% loaded BZT device.The two terminals of the PENG are connected to the oscilloscope to determine the energy harvesting from daily mechanical stress.The forward and backward switching tests were performed to find out whether the PENG's output signals originate from the piezoelectric effect or not.Fig. 5d depicts the forward and reverse bias test results of the PENG; it is clear that when the device is connected in the reverse configuration, the output signals of the forward configuration are precisely switched exhibiting high efficiency of switching and performance quality.The voltage values of PENG increases as the load resistance is increased as shown in Fig. 5e. Figure S6 (supplementary information) shows the power across various resistance.Further, Fig. 5f shows the output performance of PENG under the finger-tapping test.The output voltage is good enough to activate LCD screen.This result is depicted in Fig. 5g and supporting video 1. Figure S7 (supplementary information) shows the stability(voltage response) of PENG.Table 4 shows the comparison of PENG (BZT-PVDF-HFP) output voltage with literature

Electrochemistry
Another interesting application of BZT ceramic is its capability to promote hydrogen evolution reaction (HER).Figure S8 (supplementary information) shows the schematic of water splitting.The HER performance of as prepared BZT is tested in the N 2 saturated 0.5M H 2 SO 4 and 1M KOH electrolytes.Figure 6a-d shows the HER performance and corresponding Tafel plots of BZT measured in 0.5M H 2 SO 4 and 1M KOH electrolytes with a scan rate of 20 mVs −1 .The observed over potentials are compared with commercially obtained Pt/C.From the plots it is evident that BZT is exhibiting higher overpotentials than the standard Pt/C electrode.BZT exhibited an overpotential of 490 mV (Fig. 6a-acidic medium) and 574 mV (Fig. 6c-alkaline medium) at standard 10 mA cm −2 , while Pt/C exhibited 42 mV (Fig. 7a-acidic medium) and 102 mV (Fig. 6c-alkaline medium) at standard 10 mA cm −2 .The obtained overpotentials for hybrid microwave sintered BZT are extremely superior to previ- ous reports [59][60][61][62][63] .Table S3 shows the Tafel slope values comparison with literature.The electrocatalytic activity is plausibly explained based on Tafel slopes.Figure 6b,d exhibits the Tafel slopes for the microwave sintered BZT and commercially obtained Pt/C working electrode.The results once again confirm the superior nature of BZT as a electrochemical catalyst.The Tafel slope of BZT in the acid medium is 77 mV dec −1 as compared to 41 mV dec −1 of Pt/C.Though the variation in alkaline medium is very less, i.e., it is 166 mV dec −1 for BZT and 152 mV dec −1 for Pt/C electrode.BZT is found to be rapidly reactive in acidic medium than in alkaline medium.The observed small Tafel slope of 77 mV dec −1 is attributed to rapid electron transport through the interfacial planes of BZT.Further, it is noteworthy that the slope of 77 mV dec −1 is the lowest of the ferroelectric ceramics    www.nature.com/scientificreports/ reported till date.The hydrogen evolution reaction (HER) mechanism can be analyzed based on Volmer (> 120 mV dec −1 ), Volmer -Herovsky (> 120-40 mV dec −1 ) and Volmer-Tafel (>40 mV dec −1 ) kinetics [64][65][66][67] .This reac- tion kinetic resembles the probable H-atom adsorption and desorption mechanisms to enrich the HER activity of the prepared catalyst.From the obtained Tafel slopes Pt/C electrode follows Volmer Tafel kinetics while BZT follows Volmer Herovsky.The sample is tested for CV cycles and is followed to be retracing the cycle for 2000 cycles.The stability of the catalyst is estimated by the polarization curves (LS -linear sweep voltammetry) before and after the 2000 CV cycles.The LSV curves coexists with after 2000 cycles of CV.This test confirms the stability of BZT as a catalyst.The results are presented in the supplementary (Fig. S9, Supporting Information).

Discussion
In summary this manuscript reports the microwave sintering of BZT and its applications.The XRD refinement studies confirm the tetragonal crystal structure with the goodness of fit 2.48.The dielectric constant is found to be 6740 with a low dielectric loss of 0.65 at a frequency of 1KHz.The PE loop shows the moderate energy storage efficiency of 30.7 %.In order to show that BZT have a rapid reaction mechanism and excellent catalytic activity, electro chemical studies are performed.A Tafel slope of 77 mV dec −1 is observed for the acid medium.Furthermore, electrospun PVDF-HFP-BZT mats were used to make a flexible PENG device.Electrospinning effectively resulted the composite fibres with higher percentage of beta phase of PVDF-HFP -BZT.

Methods
Barium zirconium titanate (BZT) ( BaZr 0.02 Ti 0.98 O 3 ) and BT are synthesized by using regular solid-state double sintering method.To synthesize the BZT ferroelectric phase, the compositional powder materials, BaCo 3 (Aldrich 99.99%), TiO 2 (Aldrich 99.99%), ZrO 2 (Aldrich 99.99%) are weighed in a suitable stoichiometric ratio and milled in a zirconium bowl using zirconium balls and acetone as grinding media for 8 hrs at 400 rpm in the high-energy planetary ball mill (PULUERISETTE-6).After milling, the slurry is dried at 60 • C for 2 hrs.The obtained powder is compacted by cold pressing and calcinated at 1000 • C (BZT and BT) for 20 min in an alumina crucible using a hybrid microwave furnace (VB Ceramics Pvt. Ltd.India).After that, the calcinated powders were milled at 8 hrs in an acetone medium.The slurry is dried and seaved using 10-micron mesh to get uniform powders.These homogeneous powder is added with a small drop of PVA for the pellet preparation.The set of green pellets (10 mm dia and 1mm thickness) are sintered in hybrid microwave furnace at 1300 • C (BZT), 1250 • C (BT) for 30 min in an open-air atmosphere.

Electrospinning of BaZrTiO 3 /PVDF-HFP Nanofibers
To make the electrospinning solution, a mixture of DMF and acetone was used as a solvent.At first, PVDF-HFP is mixed into the solvent at a rate of 500 rpm for 2 hours at a temperature of 60 • C. The next step involves adding BZT powder to the transparent PVDF-HFP solution see in Fig. 7a,b.The solution is sonicated for 1 h to make a homogeneous solution.The ceramic weight percentage in the composite (BZT/ PVDF-HFP) series is set to 0, 8, 16, and 24 wt%.Initially, the metal needle is fixed at the end of the 10 ml plastic syringe.The homogenous formulated composite ink is filled with the syringe.Parameters for electrospinning include a 20 kV applied voltage, a drum speed of 1500 rpm, and a 1.25 ml/hr flow rate.Typically, there is about 15 cm gap is maintained between the drum and the needle.The fibres produced by electrospinning are collected on a collector.The collector is wrapped with the Al foil.See in Fig. 7c.Before characterization, the collected fibres are dried in vacuum at room temperature.The BZT/ PVDF-HFP series has ceramic weight percentages of 0, 8, 16 and 24 wt%.

Data availibility
The corresponding author can provide the datasets used and/or analyzed in the current work upon reasonable request. Vol

Figure 1 .
Figure 1.(a) Rietveld analysis for BZT indicates phase formation of BZT (b-d) An XPS image of the Ba-3d orbital states performed at a high resolution.Evidence of Zr can be found at the Ti-site in the Ti-2p state.The energies of the Zr-3d states contribute significantly to the range that spans from 180 to 184 eV.(e) High resolution scan close to the binding energy of Oxygen peaks.The peaks at 529.27 eV and 530.61 eV are attributed to O 2− , O 1− , and the chemically adsorbed oxygen ions.
. At room temperature to 110 • C the BZT shows tetragonal phase, which on further heating (greater than 110 • C) transforms into the cubic phase.The ferroelectric to para electric transition (tetragonal to cubic) of BZT-1250, BZT-1275, BZT-1300 are 118, 114.108 respectively.It is shown in Fig.3a,b.The T c of BZT is lesser than BT the reason is the Substitution of Zr ion in the B site.FigureS4a,b (supplementary information) depicts the frequency-dependent relative permittivity and tand of BZT1300 which are in the range of 1 K to 1M.The microwave sintering temperature of BZT-1300 • C for 30 min appears to be optimal for producing high-quality BZT ceramic.

Figure 2 .
Figure 2. (a,b) Variation of dielectric constant and loss with varying temperatures at 1kHZ, 10kHz and 1MHz frequency follows the trend.The details are given in the text (c) P-E loops of BZT-1300 at various electric fields indicates the ferroelectric nature of BZT along with its capability to be utilized as energy storage device (d-g) energy storage properties for BZT-1300, the loop area gives the loss energy characteristics and the remaining area reveals the recoverable energy of the material.
www.nature.com/scientificreports/Ferroelectric studies P-E hysteresis loops are specific to ferroelectric materials and are used to verify the electro ceramics' ferroelectricity.Figure2cdepicts the P-E loops of microwave sintered (1300) BZT ceramics at various electric fields.The P r and E c values can be found using ferroelectric hysteresis loops (P-E).The final polarisation values are almost never as high as predicted.Because the polarisation is dependent on the motion of the domain walls, the reorientation, and the switching between domains.The internal stress, as well as the internal bias electric field both, have an effect on the domain mechanism.The remanence polarization P r of 3.47 µC/cm 2 and the lowest coercive field E c of 2.26 kV/cm are recorded for the BZT-1300.Sharp edges of the PE loop of the present BZT indicate high resistivity, while round edges (lossy loop) indicate low resistivity.The square shape of the ferroelectric P-E hysteresis loop is characteristic of perfect ferroelectric material.Equation (2) can be used to determine the P-E hysteresis loop's squareness (R sq ).For an ideal case, the R sq value of the PE loop is 2. In the present work, the microwave-sintered BZT (1300 • C) ceramics have an R sq value of 0.58.

Figure 3 .
Figure 3. (a,b) FTIR spectra for BaZr 0.02 Ti 0.98 O 3 /PVDF-HFP composites with schematic illustrating zigzag TTT-conformation of the polymer chain because of interaction between the ceramic and polymer.

Figure 4 .
Figure 4. (a) Zeta potential analysis of BZT-1300 ceramics indicating the surface of BZT-1300 is negatively charged (b,c) SEM images for microwave sintered BZT with distorted grains with average grain size of 2.7 µ m and electrospun interwoven BZT nanofibers with average diameter in micron range (d-i) Elemental mapping for electrospun BZT nanofibers.

Figure 5 .
Figure 5. (a,c).(a) Schematic of PENG working mechanism.When an external force is applied to a crystal, it results in the displacement of anions and cations, leading to the creation of an electric dipole moment.This dipole moment can then generate a voltage differential in the direction of the applied tension within the material.The phenomenon described enables the conversion of mechanical force into electricity, and vice versa (b) Time dependent output voltage (Voc) of the PENG device at various wt% of BZT (0,8wt%, 16wt%, 24wt%) (c) Time dependent output current of the PENG device (d) Output voltage of reverse and forward connections of PENG (e) Effect of external load resistance on the output of the PENG (f) Finger tapping (g) Photographic image of LCD.

Figure 7 .
Figure 7. Schematic representation for (a-c) preparing BZT nanofibers using electrospinning which gives a high pace output at low cost.Producing micron-sized yarns that are made of nanofibers at a rate of 70 meters per minute allows for the formation of a variety of different assemblies (d-e) PENG device fabrication involving electrode installation and PET encapsulation steps.

Figure 7d -
Figure7d-e shows the schematic of a PENG device with BZT/PVDF-HFP composite film.PENG is fabricated by slicing the electro spun flexible film to the required sizes.Two flexible Al sheets attached to both sides of the film will act as electrodes.To measure the output performance of the flexible device (PENG), copper wires are pasted on Al electrodes using conductive epoxy.The flexible adhesive PET sheet is fixed on both sides of the devices.This will eliminate the gaps between the electrode and PET sheet to avoid the triboelectric effect and protect the device from the surrounding atmosphere.

Table 1 .
Comparison of the binding energy of elements between the present work and the literature. S

Table 3 .
Comparison of output performance (energy storage efficency) of the BZT with the literature.

Table 4 .
Comparison of the synthesis technique and output performance of the PENG with the literature.
Vol.:(0123456789) Scientific Reports | (2024) 14:2650 | https://doi.org/10.1038/s41598-024-52705-0www.nature.com/scientificreports/ The piezoelectric outputs of the PENGs are greatly improved by the hybridization of negative surface charge on BZT ceramic particles and positively charge hydrogen in PVDF -HFP polymer.The open-circuit voltage, short circuit current and power of the nanocomposite fibre PENG with 16 wt% BZT exhibited 7Vpp, 750 nA and 2.5 µ W under the mechanical force of 3 N.Furthermore, the voltages are developed by finger tapping 2 Vpp and LCD display could be switched 'ON' .The feasibility studies present energy storage, energy conversion, and energy harvesting applications presenting great potential of the environmentally friendly BZT-based materials to be integrated in a wide range of applications.